'Teacher Toads' Train Predators to Stay Away

May 7, 2008

Setting cane toads loose in areas of Australia that don’t already have them may sound like a crazy idea, but research by the University of Sydney’s Professor Rick Shine suggests this could lessen the toad’s impact.

Professor Rick Shine, winner of the prestigious Macfarlane Burnet Medal and Lecture, will present his findings on 7 May at the Australian Academy of Science’s Science at the Shine Dome event in Canberra.

The cane toad, Bufo marinus, is a huge pest in eastern Queensland and is rapidly spreading westwards across the Northern Territory into Western Australia, and south through New South Wales.

One of its biggest impacts is killing native Australian animals that eat the poisonous toad. Populations of the Northern Quoll, a threatened species, have been decimated by eating cane toads, as have native goannas, snakes, and freshwater crocodiles.

“We’ve had no effective way to stop the impact of cane toads on our native fauna,” said Professor Shine. “The problem is that all of the toads at the invasion front are very large animals – so large that when a predator attacks one, it is exposed to a lethal dose of poison.

“But if the first cane toad that a predator encounters is a small one, it can survive the experience and learn to stay away from other toads. So we can teach native animals to stay away from cane toads, by giving them a scare with a smaller, less poisonous cane toad, and reduce the number of native animals dying.

“Small toads could be dropped into areas in advance of the spreading cane toad front, to act as ‘teacher toads’ for native animals. Native animals survive their first encounter with the cane toads, but get slightly ill and learn to keep away.

“To stop these ‘teacher toads’ becoming a menace in their own right, we can use sterile male toads for this purpose – toads that are unable to reproduce. Producing sterile male cane toads in large numbers is straightforward, due to research by Professor Michael Mahony at Newcastle University.”

Professor Shine and his research group, Team Bufo, have collected detailed data on the effectiveness of ‘teacher toads’ on native fish, frogs and marsupial predators, but more work needs to be done with reptiles.

“Native frogs, fish and mammals learn very quickly when they encounter the ‘teacher toads’, but we need to do more research with snakes,” said Professor Shine.

In his Macfarlane Burnet Lecture, Professor Shine will also unveil a critical piece of new information in the fight against the toad. His team has been studying parasitic lung worms, that are capable of killing toads in large numbers, but ideas about using the parasite to control toads have been stymied by the risk that the parasite would also attack native frogs. The parasite was thought to be an Australian species that has shifted from frogs to cane toads – and so might easily shift back again.

“Our new genetic studies show that the parasite in Australian cane toads is not an Australian species at all – instead, it’s a South American lung worm that came here with the toad, and does not attack Australian frogs. This is great news for reducing the number of cane toads – we can use the South American lung worm as a biological control and be sure that it will not infect native frogs.

“Using both methods together will decrease the number and impact of cane toads in Australia,” said Professor Shine. “Community groups, who are already at the frontline fighting cane toads, could implement these tactics in the future, because they are passionate about controlling toads and are good at organising action.”

Professor Shine has set up a special website: www.canetoadsinoz.com, to explain his new ideas in toad control.

The Macfarlane Burnet Medal and Lecture, awarded by the Australian Academy of Sciences, recognises excellent scientific research in the biological sciences. Professor Rick Shine received the award in recognition of his outstanding and influential research history in ecology, evolution and conservation spanning over 30 years. Professor Shine’s influence on Australian vertebrate biology is unparalleled and has transformed the fields in which he works.